The process known as horizontal directional drilling is utilized to install a variety of underground utilities in a manner that does not disrupt the surface. In use, a drill machine is used to drill a pilot bore that extends beneath the ground surface from an entry hole at the ground surface (i.e., a starting point) to an exit hole at the ground surface (i.e., an ending point). The pilot bore is drilled by rotating and pushing a ground engaging tool (e.g., a drill bit) that is attached to the end of a drill rod. The length of the pilot bore is extended by stringing multiple rods together to form a drill string. The direction of drilling can be controlled (i.e., the drill string can be “steered”) by various techniques to control the depth of the pilot bore as well as the location of the exit hole. The location of the drill string, after the pilot bore is completed, represents the desired location of the utility to be installed.
After the pilot bore is drilled, the drill bit is typically removed and a second ground engaging tool installed onto the end of the drill string. This tool is typically known as a back reamer or a hole opener. Its function is to ream/open the drilled bore to a diameter sufficient to allow installation of the utility. To provide a reaming function, the back reamer is typically pulled back through the pilot bore by the drill string as the drill string is withdrawn from the pilot bore. Oftentimes the utility being installed is attached with a swivel located at the end of the back reamer such that the utility is pulled into the reamed bore immediately behind the back reamer. (See FIG. 1.) In this way, the act of withdrawing the drill string will simultaneously result in the installation of the utility.
The type of utilities installed typically includes telecommunications, power, water, natural gas, liquid gas pipelines, potable water pipes and sewers. Due to this large variety of utilities, there is a large variety in the size requirements for the final reamed borehole, and thus a wide range of back reamer sizes is required.
Back reaming can be of the type that includes a plurality of roller cones attached to a tool body. For an example of such a back reaming tool, see U.S. Pat. No. 7,243,737, which is incorporated by reference herein it its entirety. There is a need for improved back reamers that are configured to withstand extreme use conditions and are easily rebuildable.